The applicants hereby claim the benefit of priority of German Application No. 100 41 254.8, filed Aug. 23, 2000. The entire contents of this German application are incorporated herein by reference.
The invention relates to a shutter for a photographic camera, having a first and a second pretensioned shutter curtain which are respectively retained in the tensioned state by a first and a second pivotably mounted retaining latch in interaction with a first and second curtain latch, the first retaining latch being coupled to a camera release for enabling release of the first curtain, and the second retaining latch being coupled to a release device, which is controlled as a function of the release of the first curtain, for enabling release of the second curtain.
For the temporally controlled exposure of film, cameras have, in front of the plane of the film, a shutter which comprises two curtains moving temporally one after the other. The curtains can be formed by metal plates or rolling cloth screens. With the transport of a film into the exposure area, both curtains are tensioned via a spring mechanism and are retained in this state by a latch and lever mechanism. In the case of an electromechanical design, the curtains are retained by magnetically actuated latches.
Purely mechanical spring-tensioning and latch/lever mechanisms have the advantage that they are independent of an electric power supply and are operative over a large temperature range. However, the mechanical requirements and the outlay on components for the timing between the start of the first shutter curtain and the start of the second shutter curtain are considerable, particularly for relatively short shutter times. For the release of the latches, high frictional forces have to be overcome. When the second shutter curtain is released through the movement of the first curtain, the latter is briefly retarded, with the result that the times formed become imprecise. In the case of very short shutter times, this leads to difficulties in coordinating the mechanical elements and forces.
Retaining magnets for the shutter curtains have the advantage of permitting an electrically controlled first release and an electronic timing which is based on the latter. The movements of the two curtains can be controlled independently of each other. However, the high energy requirement of the retaining magnets is disadvantageous in some designs.
The invention is based on the object of making selective use of the advantages of both shutter releasing designs. In a camera having a purely mechanically controlled shutter release, the intention is to be able to use the existing mounting space for the mounting of solenoids to reduce the complexity of the components for a mechanical timer mechanism. The shutter release itself can be a common camera release.
In the case of a shutter of the type mentioned at the beginning, this object is achieved according to the invention in that the first and second retaining latches are respectively assigned first and second movement-releasing active surfaces which are each coupled either to a mechanically controlled or an electronically controlled curtain-release enabling arrangement. Advantageous refinements and developments are described below.
The curtain latches, which are under spring stress after the setting of the shutter are locked via a respective, pivotably mounted retaining latch. The retaining latches are respectively assigned active surfaces which are separated geometrically from each other and via which the locking of the latches can be selectively released. The active surfaces are advantageously provided directly on the retaining latches. The retaining latches can first of all be designed in a simple manner in terms of their size to provide vibrationproof locking of the curtain latches. They moreover form a lever whose length and shape can be selected independently thereof in such a manner that, in the event of an impact against one of the active surfaces with sufficient force, reliable release of the latch connection takes place.
One of the active surfaces in each case can be assigned to a purely mechanically controlled release of the latch, while the other active surface can be assigned to an electronically controlled release of the latch. The mechanically controlled release of the latch contains a mechanical chain of action at whose end an unlatching lever acts upon the assigned active surface on the first retaining latch by means of impact or pressure. The electronically controlled release of the other latch contains a solenoid having a dischargeable armature lever which can be pushed against the respectively other active surface. The mounting space required for these components is relatively small.
For the selective setting of the two release options an eccentric is provided with which the mechanical chain of action can be moved into the functional position or moved out of the functional position. The eccentric is expediently coupled in this case to a mode selector switch. In a position in which the eccentric brings the mechanical chain of action into a functional position, the power supply for the solenoids can be interrupted in a simple manner via the actuation of a switch, with the result that double releases are reliably avoided.
The eccentric also enables the mechanical chain of action to be moved into functional positions which are coupled to a mechanical timing assembly for the successive release of the latches. For this purpose, the curtain latch which is released first of all can be designed as a cam plate which, as a function of the particular position of a control lever for the curtain latch to be released subsequently, acts at an earlier or later point on said control lever. The accuracy of this setting of the shutter times is limited, but is entirely sufficient for standard times.
Pulsed magnets are advantageously provided as electrically activatable solenoids. Said pulsed magnets are distinguished in that their armature lever is retained in the currentless state by permanent magnets and the armature is discharged only when sufficient power is supplied. The load on the power source in the camera is therefore kept very small. However, it is disadvantageous that in the event of discharging of the armature released first and a subsequent disconnection of the power supply prior to the discharging of the armature to be released subsequently, the associated shutter curtain remains open. This would lead to faulty exposures. According to the invention, the on/off switch on the camera is therefore of two-stage design, so that prior to a disconnection of the power supply after power has been supplied to the first pulsed magnet, power is furthermore supplied to the second pulsed magnet.
For the precise release of pulsed magnets the design-specific value of the discharging current has to be built up as rapidly as possible. If precisely the voltage of the discharging current is applied to the magnet, then the buildup of current lasts too long on account of existing inductances. If, in contrast, a higher voltage is applied to the magnet, then the discharging current will be passed in a short time and then exceeded. As a result, the magnet builds up force again and the discharging of the armature is suppressed or becomes imprecise. According to the invention, a power supply is therefore selected which has a level profile which begins with a sharply rising signal level lying clearly above the customary discharging voltage and then drops rapidly to the design-specific discharging value.